Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $195.61   11.258%   $217.6318   $217.63   $217.65   $217.60  
  Purchase #2 $241.49   12.234%   $271.0339   $271.03   $271.05   $271.00  
  Purchase #3 $74.43   11.238%   $82.7944   $82.79   $82.80   $82.80  
  Purchase #4 $37.48   11.258%   $41.6995   $41.70   $41.70   $41.70  
  Purchase #5 $58.34   3.465%   $60.3615   $60.36   $60.35   $60.40  
  Purchase #6 $139.25   3.125%   $143.6016   $143.60   $143.60   $143.60  
  Purchase #7 $52.58   13.437%   $59.6452   $59.65   $59.65   $59.60  
  7 purchase totals = $799.18       $876.7679   $876.76   $876.80   $876.70